Technical Field
The present invention relates generally to voltage regulation using Grid Energy Storage (GES), and more particularly, to a system and method for regulating voltage using GES to provide voltage support and to enhance power system voltage stability.
Description of the Related Art
Grid-connected energy storage systems (ESSs) are a fast growing global market. Recently, increases in the penetration of renewable energy resources into grid-connected ESSs have presented a challenge to the traditional design and operation of electric power systems. The existing power grid was designed for centralized power generation with unidirectional power flow. With renewable energy (or any other type of distributed generation of electricity), power is effectively generated everywhere and flows in multiple directions. However, the intermittent and highly variable nature of distributed generation causes power quality and/or reliability issues, which leads to increased energy costs. Furthermore, a critical problem is a wide variation of system voltage. For example, as the load continues to increase, utilities attempt to push the grid to transfer more and more power.
In conventional systems, power flows in a single direction from substation to the remote end, and the voltage level drops along the distribution feeder. However, with high penetrations of PV generation, power flow and voltage profiles in a distribution system change significantly over time. When PV generation substantially exceeds local load at the point of common coupling (PCC), surplus power from the PV will flow back to the grid and produce reverse power flows, which causes a voltage rise problem. Furthermore, because of the high variability of solar energy availability (e.g., cloud transient effect), PV generation may fluctuate at a very high ramping rate, which may cause severe power quality and voltage stability issues.
Conventionally, load tap changers (LTCs) are employed to regulate voltages in distribution systems. However, LTCs have a typical delay time of at least 30 seconds, which cannot solve a voltage fast fluctuation problem caused by, for example, PV arrays. Several methods have been attempted to tackle the voltage fluctuation and voltage instability issues, (e.g., curtailing power output from renewable power plants when grid voltage exceeds limits, performing reactive power compensation to elevate or lower voltage, performing active network management, and under voltage load shedding (UVLS) methods). However, no conventional systems or methods effectively and economically regulate and/or stabilize voltage in the power grid.